1. Field of the Invention
The present invention relates to a surface treatment apparatus for printed sheets that enhances the added value of a printed sheet of paper by pressing a transfer film onto the printed sheet, thus transferring gold foil, embossed pattern, hologram pattern, etc. on the transfer film.
2. Related Art
There was proposed a gloss-finishing machine that enhances the added value of a printed sheet of paper (hereinafter referred simply to as “printed sheet”) in the manner mentioned above. This machine includes a varnishing unit for applying UV (ultraviolet) cure resin varnish, and a hologram forming unit for pressing a transfer film onto a printed sheet having varnish applied by the varnishing unit, thereby transferring hologram pattern or the like on the printed sheet. The hologram forming unit includes an impression cylinder for conveying printed sheets, a pair of pressing rollers for pressing a transfer film onto each printed sheet on the impression cylinder, a UV radiation part for curing varnish when the transfer film is kept pressed onto the printed sheet on the impression cylinder by the pair of pressing rollers, and a shutter means disposed forward of the radiation side (downside) of the UV radiation part for being shifted between a retracted position at which UV rays from the UV radiation part are allowed to be radiated onto a printed sheet, and a shuttering position at which UV radiation from the UV radiation part is cut off. The pair of pressing rollers are arranged to be movable towards and away from the impression cylinder between a retracted position above the impression cylinder and a pressing position at which they are positioned close to the impression cylinder. With this arrangement, when hologram forming (surface treatment) is not carried out, the pressing rollers are positioned at the retracted position above the impression cylinder while at the same time the shutter means is shifted to the shuttering position, thereby preventing UV rays from being radiated onto the printed sheet (cf. Patent Document 1, for example).
(Patent Document 1) Japanese Patent Application Laid-open No. 2006-315229
According to the above gloss-finishing machine of the Patent Document 1, a special shutter means is necessitated, which causes not only the increase in the number of parts, but also makes it impossible to dispose the UV radiation part sufficiently close to the impression cylinder due to the necessity to dispose the shutter means between the impression cylinder and the UV radiation part. Therefore, UV rays radiated from the UV radiation part may not be able to be efficiently utilized and hence a large-sized high-performance UV radiation part must be used, which causes increase in the size of the machine as well as a disadvantage in terms of cost. When hologram forming is not carried out and no shuttering means is employed, the UV radiation part may be structured to be switched on and off so that UV rays are not radiated onto the printed sheet when the UV radiation part is switched off. However, since it is likely that the UV radiation part cannot be immediately turned into operation when it is switched again from off to on, the operation efficiency may be deteriorated and therefor this method is difficult to be employed in actual operation.